Torque converters have been utilized as an interface between a motor vehicle engine and transmission in order to conveniently achieve fully automatic operation and to increase the axle torque at vehicle launch. As the vehicle approaches a steady state operating point, however, the inherent slippage of the torque converter degrades fuel economy, and a fluid operated torque converter clutch (TCC) is engaged to provide a mechanical coupling between the engine and the transmission.
In practice, it is convenient to schedule engagement of the TCC as a predetermined function of vehicle speed (and engine load) to obtain a proper balance between driveability and fuel economy. At low vehicle speeds, open converter operation (TCC disengaged) is required to avoid lugging or stalling the engine, while at higher vehicle speeds, closed converter operation (TCC engaged) is desired to optimize fuel economy.
With the advent of electronic controls and the consequent ability to more accurately control the torque capacity of the TCC, it is possible to apply the TCC more extensively without adversely affecting driveability. In addition to providing fuel economy gains, early TCC engagement can also provide performance improvements under certain conditions.